District switching circuits for telephone systems



1957 H. TOPFER ETAL 2,803,705

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DISTRICT SWTTCHING CIRCUITS FOR TELEPHONE SYSTEMS Filed Dec. 17, 1951 r 4 Sheets-Sheet 4 INVENTORS Herban T'cipfer Erich Ehricka Alois Brqndstefier Alfo Peissner ATTORNEY Unitcd States Patent DISTRICT SWETCHIWG CIRCUITS FGR TELEPHONE SYSTEMS Herbert Tiipfer, Erich Ehricke,

Alfons Peissner, mens & Halske Germany,

Alois Brandstetter, and

Munich, Germany, assianors to Sie- Ahtiengesellschaft, Munich and Berlin, a corporation of Germany This invention is concerned with district switching circuits for telephone systems.

In telephone systems in which the subscribers can dial long distance over large territories, for example, over an entire country, there are connections set up over several regional networks of difierent classes or network planes. Included in these. is a class which comprises exchanges functioning as the central switching offices of regional groups. The next higher plane or class comprises main exchanges, and the top class or plane finally includes the transit toll exchanges or central exchanges of the corresponding districts. The connections are established over the various networks by means of district numbering schemes which secure the uniform numbering of all local exchanges. The main or principal guiding paths for the setting up of connections which are determined by the district numbers are not always the shortest and therefore the most economical paths over which the connections can be established. Routing methods are therefore used to utilize the available interchange trunking paths or detouring trunks in addition to the direct trunks between the individual central exchanges of the network groups.

There is a routing or detouring operation known in which a call originating in a local exchange is responsive to dialling of a toll-discriminating number routed over switches in the individual network switching offices and switched through to the central exchange. This path may then be released responsive to the dialling of a direction-determining number, and the connection may be switched over a direct interexchange trunk to the exchange which is nearest to the called party. This operation entails temporary seizure of trunks and switching equipment which may in part be very valuable.

, In order to avoid such temporary seizures, it has been proposed to provide in all switching exchanges impulse repeaters which operate responsive to receipt of the directional number to switch the routing switches to an idle interofiice trunk or regular direct trunk, and which repeat the directional number so as to set the successive switches. Some of the digits of the directional numbers, which are not needed, may in this procedure be absorbed.

The operation indicated in the preceding paragraph avoids temporary seizure of the usually high-grade (fourconductor) trunk lines and switches, but it causes delays which may be considerable. It also requires considerable expenditures, due to the necessity of providing impulse repeaters in all exchanges.

A system has become known (paper published in Fernmeldetechnische Zeitschrift, Oct. 1950, No. 10, pp. 365-371, entitled Ein Fernwahlsystem mit Richtungsvorwahl), the title of this paper meaning A Toll Selection System with Directional Preselection, which proposes to completely avoid temporary seizures as well as to reduce the expenditures in impulse repeaters. This system provides storage-repeaters merely in the network group center points of the local exchanges of a district, which are the switching points of the toll call-originating exchanges. These storage-repeaters alter the district numher dialled by the calling party and transmit a multi-digit preselection number prefixed to the district number to cause the setting up of the toll call stage by stage over the regular trunk paths, provided that no interoifice trunks are available. I f an idle interoflice trunk is foundb'y the routing switches controlled by the preselection digits, which leads to the network area of the called subscriber, the stor'age-repeaterwhich is controlled by checking inipulses skips the digits of the preselectiou' number which are not required and transmits the necessary digits of the district number. After connection is in this manner established with the terminal exchange designated by the corresponding district number, the calling party receives from this terminal exchange a signal indicating that he may now dial the called subscribers local number.

A disadvantage of this known system resides in the central location of the storage-repeater devices, that is, the location thereof as common devices for several routing switches in the corresponding switching exchanges. These storage-repeater devices are usually provided in limited numbers, and waiting intervals therefore result until one or the other device becomes available for receiving impulses, thus representing potential points of congestion.

Another disadvantage resides in the following situation: The setting of the directional switches in the individual network exchange switching ofiices must be carried out by digit sequence (the preselection number) which is produced by the storage-repeater device located in the calloriginating exchange and which is entirely different from the impulse sequence of the dialled district number. This means that all possible interofiice directions, which may be reached in setting up a given call, are numerically occupied in the storage-repeater device in the call-originating exchange. The storage-repeater or translating devices of all such exchanges therefore must provide for differentiating digit re-forming or translating schemes for the interoflice trunks. Changes in the number of the interofiice trunks are thus not limited to the corresponding routing point or ofiice, but call for changes in the storage-repeater devices of all exchanges that may make use of the concerned exchange, therefore requiring changes in the digit-numbering and re-forming schemes of the entire district.

There are additional waiting intervals caused by the centralization of the storage-repeaters and also delays due to the storage and digit re-forming operations. Further delays occur at every switching point requiring the repeating of the direction-determining re-formed digit or digits. These waiting intervals cannot be compensated since the corresponding system does not provide for auxiliary storing of the remaining digits of the subscriber numbers. The system thus enforces the introduction of a pause at the termination of which the subscriber must dial again to control the setting up of the remaining stages of the call. The termination of this enforced pause is signalled to the calling subscriber by the announcement of the desired local exchange. To the waiting time prior to the announcement therefore must be added an interval required for the announcement itself.

The invention avoids the drawbacks and disadvantages of the prior system by providing impulse repeater devices only in the toll call-originating exchanges and by trans- I mitting differentiating check-back signals from the routing points to the originating exchange, which signals, depending on the path that has been completed in the setting up of a connection, may call for the repeating of certain digits of the stored routing or district number.

These check-back signals may consist, for example, of

impulses of diiierent length, or of identical length but different in numbers, or of impulses of different frequencies, or of combinations of some or all of such impulses.

In accordance with another object, there are provided marker switches individual to the routing switches for marking the desired trafiic directions. The zoning switch provided in the call-originating exchange may serve the purpose of such a marker switch.

The system made in accordance with the invention avoids temporary seizures of any kind, as well as the necessity for intermediate storage devices or impulse repeaters in all switching exchanges which follow the calloriginating exchange, and provides in addition the following advantages:

Only the number for the marking of the desired traflic direction has to be evaluated. A special preselection number as a prefix to the district number is not required, thereby eliminating the need for revaluation or re-forming of the district number in storage-repeaters. The evaluation of the district number requires merely the marking of potentially available interotlice trunk directions at the routing ofiices. Changes in the number of interoifice trunks therefore requires only wiring changes at the routing offices, therewith considerably less work than is required in the case of the prior system which in such circumstances calls for changes in the number-evaluating devices of all call-originating exchanges that might use the concerned routing exchange.

No numerical re-forming is required by the invention, thereby obviating special re-forming schemes and avoiding limitations as to the number of interofiice trunks at each routing exchange.

Waiting intervals occur in the present system at each routing exchange for which the direction-determining marking digits of the district number have to be repeated. However, the calling subscriber can without any pause, successively dial all digits of the district number and also the digits of the called subscribers line, and the pauses incident to repeating impulses can be reduced to a minimum, thus practically compensating for the waiting intervals during the dialling operation. This is particularly true in the case of dialling numbers having many digits. The procedure eliminates enforced pauses, thus avoiding imposition of operating limitations on the subscribers.

The invention will now be described with reference to the accompanying drawings, in which Fig. 1 shows an example of a district network;

Fig. 2 shows the network of Fig. 1 in schematic circuit representation, including the switching equipment such as the selector, zoning switch, impulse'repeater means and routing switch means employed in the setting up of a toll call;

Fig. 3 is a schematic circuit diagram showing details provided in the switching oflices, in the main exchange and in the central district exchange, respectively;

Fig. 3a shows a circuit of a known impulse repeater adapted for use in the circuit according to Fig. 3.

Fig. 3b shows a relay chain for use in the circuit according to Fig. 3; and i Fig. 3c shows drive means for a routing switch employed in Fig. 3.

The network shown in Fig. 1 comprises, in its highest plane or class, the central district exchanges ZA', in its next lower plane, the main exchanges HA; and in its lowest plane, the switching offices KA. To the switching ofiices KA are connected the individual terminal or local exchanges EA. The marking numbers are in the network scheme, for example, so distributed that the digit 2 is reserved for the central district exchange ZA2 within the central exchange district ZB2; the digit 3 is for the central district exchange ZA3 in the district ZB3; and the digit 4 is for the central district exchange ZA4 in the district Z84. The main exchanges HA within the district ZB2 therefore have the marking numbers 26, 27. Switching ofiices KA that may be reached from d the main exchange HA26 have numbers comprising the digits 26 with a sufiix added, e. g., 262, 263. Corresponding numbers are provided for the main exchanges HA and switching offices KA in the districts ZB3 and ZB4.

A toll call from a subscriber of an individual local or terminal exchange, or from a subscriber directly served by a switching ofiice such as KA262 to the subscriber of another terminal exchange, for example, 3624357 of the switching oflice KA362, is set up (after the calling subscriber connects with the equipment in his own exchange KA262 by dialling the digit 0), responsive to the digits corresponding to the direction-determining number 362. This number is stored in the switching oflice KA262 and the connection is first switched directly to the interoflice trunk lines QKl leading to the switching ofiice KA362 and, if these are busy, the connection is automatically switched over the interofiice trunk lines QK2 leading to the main exchange HA36. The connection is then directed from the main exchange HA36 over the regular or principal trunk RL to the switching otfice KA362. The last digit 2 of the marking number 362 is in this latter case repeated by the switching olfice KA262 for the setting of the group selector in the main exchange HA36. No marking digit is repeated if a direct interoffice trunk QKl is used. If the interoffice trunk QK2 is also found busy, the connection is automatically switched by the routing switch in the exchange KA262 to the interoffice trunk QK3 (leading to the central district exchange ZAS), whereupon the impulse storage device in the exchange KA262 repeats the last two marking digits 62 so as to direct the call from the central district exchange ZA3 over the principal trunk RL to the main exchange HA36 and from there to the switching office 362. If all interofiice trunks are busy, the toll call is switched by the routing switch at the exchange KA262 to the principal trunk RL leading to the main exchange HA26 in which a routing switch now attempts in a similar manner to direct the connection over the interoifice trunks QHl, QH2 or QH3. In case these trunks are also found busy, the call will be switched over the principal trunk RL to the central district exchange ZA2 and from there in similar manner first over the interofiice trunks QZ1, QZ2 or the principal trunk RL to the central district exchange ZA3 and thence over the main exchange HA36 to the desired switching oflice KA362.

.The entire marking number 362 is repeated at the originating switching ofiice 262 always upon switching over of the call to a principal trunk RL to the own main exchange, or to a central district exchange in case all interoflice trunks are busy.

. In the event that the principal trunk RL to the central district exchange 2A3 should be busy after the call is switched through to the central district exchange ZA2, the routing switch in this central district exchange ZA2 will automatically switch over to a by-pass to the central district exchange ZA4 over the principal trunk RL2-4 from which the call is directed, responsive to repeating of the entire marking number, to the central district exchange ZA3 over the principal trunk RL4-3. The connection is then routed to the main exchange I-IA36 and from there to the desired switching office KA362.

The setting up of a toll call will now be explained with reference to Fig. 2 which shows the network scheme of Fig. l in schematic circuit representation, by including switching equipment such as a group selector, zoning switch, impulse repeater and routing switch employed in completing toll calls.

In accordance with the invention, there are provided in the switching office KA262 (district ZB2) a zoning switch ZS, an impulse repeater IW and a routing switch UW; The group selector GW, responsive to a trafiic-discriminating digit 0, seizes the zoning switch ZS which receives the directiondetermining marking number. In the main exspasms change HA26 there is provided for the through traflic only one routing switch UW; in the LCI1tI3l district exchange ZA2 there is provided the group selector ZGWI and a routing switch UW. For the setting up of toll calls originating in the main exchange HA26 (by subscribers directly connected thereto or by subscribers connected to sub-exchanges thereof), there are again provided a zoning switch ZS, an impulse repeater IW and a routing switch UW. The same is true so far as the central district exchange ZAZ is concerned, which provides for the setting up of originating toll calls the group selectors GW and ZGW2, the zoning switch ZS, the impulse repeater IW and the routing switch UW. It is assumed that there are no inter-oflice trunks leading to the central district exchange ZA4, and there are therefore mixing switches MW provided which give the possibility of switching over, to route calls over by-pass connections.

In the case of a toll call originating in the switching office KA262, or in a sub-exchange thereof, and directed, for example, to the subscriber 3624-357 connected to the subexchange EA of the switching ofiice KA362, the group selector GW in the ofiice KA262 will respond to the trafiic-discriminating digit and will seize the zone switch ZS. The calling subscriber dials without any interruption all the digits of the Wanted number. Of these digits, the direction-determining number of digits 362 are stored in the zoning switch ZS. The remaining digits are stored in the impulse repeater IW which is preferably formed as a mechanical impulse repeater. The storing of the marking number or digits in the zone switch marks the desired traffic direction in the associated routing switch. The latter becomes operative after the storing of the marking digits and hunts first for an idle interotlice trunk QKI leading to the switching oflice KA362. If an idle trunk is found, the impulse repeater IW will immediately transmit the digit 4 required for the setting of the group selector EGW, and then the three digits 357 of the called subscribers number, which are eflective in the sub-exchange 3624 to set another group selector and the connector, respectively, so as to complete the call.

In case there is no idle interoffice trunk QKl leading directly to the switching otfice KA362, the routing switch UW will hunt for an idle trunk in the group of trunk lines QK2 which connect with the main exchange HA36. There is provided a special step between the two bank contact groups in the routing switch, the so-called checkback step over which is controlled the transmission of a check-back signal to the zone switch. The check-back signal prepares for the re-transmission of the last digit of the marking number by the zone switch, provided that the routing switch finds an idle trunk in the next successive group of inter-ofiice trunks. The last digit of the marking number repeated by the zone switch ZS, which in the assumed example is the digit 2, causes the group selector KGW in the main exchange HA36 to connect with an idle principal trunk leading to the desired switching oflice KA362. The impulse repeater IW thereupon transmits the remaining digits of the called subscribers number.

If there is no idle interofi'ice trunk to the main exchange HA36, the routing switch in the call-originating switching ofiice KA262 will continue hunting in the group of interofiice trunks QK3 leading to the central district oflice ZA3. Upon transition from one group of trunk bank contacts to the other, the routing switch will again pass over intermediate check-back contacts lying between the two bank contact groups. Over these check-back contacts is controlled the transmission of a check-back signal, for example, a brief current impulse to the zoning switch of the call-originating office KA262, which prepares for the transmission of the two last digits 62 of the marking number, provided that the routing switch finds an idle trunk in the next successive trunk group. The digit 6 causes the group selector HGW in the central district exchange 2A3 to be set upon a principal trunkRL to the main exchange HA36, thereby seizing a trunk selector KGW. This latter switch is then set 'by the digit 2 to seize a principal trunk line RL to the desired switching oflice KA362, thereby seizingthe group selector EGW. The succeeding digits transmitted by the impulse repeater are used to set the final group selectors in the desired switching ofiice KA362 and the switches in the desired local exchange of the called subscriber.

However, if there is no idle trunk line to the central district exchange ZA3, the connection will be built up over the principal trunk line RL to the main exchange HA26 (of the calling partys district exchange region) to which the routing switch in the call-originating switching otfice KA62 switches over afterfinding all interofiice trunks busy. A check-back signal is transmitted to the zoning switch ZS in the call-originating ofiice KA262, when the routing switch passes from the bank contacts of the interoflice trunks QK3 to the bank contacts of the principal trunks RL leading to the associated main exchange. This check-back impulse prepares for the transmission of the digits 362 of the whole marking number, provided that the routing switch finds an idle principal trunk RL to the main exchange HA26. The series of impulses corresponding to the whole marking number 362 is transmitted by the zoning switch in the call-originating ofiice KA26 2 when the routing switch in such exchange has seized an idle principal trunk line, thereby seizing a routing switch UW in the main exchange HA26. This number is stored in the corresponding routing switch by an associated coacting rotary switch, so as to mark the desired traffic direction. After receiving the marking digits, the routing switch UW in the main exchange HA26 operates and in similar manner (like the routing switch in the exchange KA262) successively hunts for an idle trunk in the interoffice trunk groups QHI, QH2, QH3, and finally in the group of principal trunk lines RL leading to the central district exchange ZA2. A check-back signal is again given to the call-originating switching ofiice KAI262 always at the transition by the routing switch from one trunk line group to the next, so as to prepare for the subsequent transmission from the call-originating oflice KA262 of the digits corresponding to the required marking number, depending of course on the seizure by the routing switch in the main exchange of an idle interoflice'trunk line to the desired switching oiiice (KA362), or to the main or central district exchange, or seizure of an idle principal trunk to the associated central district exchange, respectively.

A central group selector ZGWI is taken into use when the routing switch UW in the main exchange HA26 seizes an idle principal trunk line RL to the central district exchange 2A2. The zoning switch ZS in the calloriginating office KA262 re-transmits the entire direction-determining marking number 362 upon termination of the hunting period of the routing switch UW in the main exchange HA26. The first digit 3 sets the central district exchange group selector ZGWl upon a routing switch UW. The latter has access to interofi'ice trunks QZ1 leading directly to the desired switching ofiice KA362, as well as to trunks QZ2 leading to the main exchange HA36, and also has access to principal trunks RL leading to the central district oflice ZA3. The second and third digits, 6 and 2, of the direction-determining marking number are stored in the routing switch UW of the central district exchange ZA2. The first digit 3 has been absorbed in the setting of the central group selector. The switching operations: which take place incident to the hunting of trunk lines to the marked switching ofiice KA362 are analogous to those which take place in the hunting of trunks in the main and switching exchanges, respectively. Depending upon the path over which the connection was built up, whether over. direct interofiice trunk lines orover by-pass trunks there will be given differentiated check-back signals, or such signals will be omitted. In the case under consideration there will be transmitted check-back signals in the form of corresponding numbers of impulsesin intermediate positions of the bank contacts groups-back to the call-originating office KA262, which call for the re-transmission of the digits of the marking number, depending on the path selected for building up the call.

If the routing switch. in the central district exchange ZA2 finds that the interofiice trunks to the desired switching otfice KA362, as well as to the main exchange HA36, and also the principal trunks to the central district exchange ZA3 are busy, it will test a by-pass connection over the principal trunk RL2-4 to another centrral district ofi'ice ZA4. Upon transition over the three different bank contact groups, there will be transmitted back to the call-originating ofiice KA262 a corresponding number of digits (three), whereby the zoning switch in this call-originating oifice KA262 is caused to re-transmit the entire marking number, beginning with the digit 3. The first digit is required for the setting of the group selector ZGW in the central district exchange ZA4. Thereupon are transmitted the marking digits 6 and 2 for the setting of the group selectors in the main exchange and in the desired switching office, and the impulse repeater IW finally transmits the remaining digits. The scheme described above assumes that there are provided interofiice trunks going from all network points in all three network planes or classes, that is to say, going to the switching office, to the main exchange and also to the central district exchange. The routing switch operates to hunt for an idle interofiice trunk to the switching ofiice after the third digit. If there is no idle interofiice trunk to the switching ofiice, the switching over takes place after the second digit, provided that an idle interoffice trunk is available to the main ex change of the corresponding district. If there is no such interofiice trunk to a main exchange, the operation of the routing switch starts after the first digit. In order to reconcile the transmission of the current impulses in these cases with the demand therefor and to utilize transmitted impulses for the at least partially without repeating, the interofiice trunks to main exchanges (in the region of which there are no interoffice trunks to switching ofiices) and interoffice trunks to central district exchanges (having no interoflice trunk-s to their switching ofiices and main exchanges) are placed in the bank multiple of the routing switch ahead of the check-back contacts. If there are no interoffice trunks to the switching ofiices, but interoffice trunks to the main exchanges and tothe central exchanges of the same region, the lines to the central exchange will be connected ahead in the bank multiple of the routing switch, by one check-back contact, so that the trunks to the main exchanges are found in the first bank contact group and the trunks to the associated central exchange in the second group.

The circuit details provided in the call-originating switching ofiice, in the main exchange and at the central district exchange, respectively, which are required for an understanding of the invention are apparent from Fig. 3, some details incorporated in Fig. 3 being indicated separately in Figs. 3a, 3b and 3c.

The zoning switch ZS, which is in the switching office KA262, comprises a motor switch having the field coils M1, M2 and having a plurality of wipers, and a rotary switch having a stepping magnet Dg (see also Fig. 3a) for the control of the zones and the storage of the first three series of impulses, which are the impulses of the directiondetermining marking number. The first two series of impulses are simultaneously received by stepping magnets D1 and D2 of two associated rotary switches (see also Fig. 3a). The latter serve with the rotary switch having the magnet Dg for the transmission of the series of impulses which are to be repeated. It is possible to use, in place of separate rotary switches, additional wipers of the motor switch for the re-transmission of the series of current impulses. I

. The incoming dial impulses are in usual known manner received by the line relay A (see also Fig. 3a) which is connected to one of the line conductors. The first series of impulses is transmitted by contact al of the relay A to the two field coils M1, M2 of the motor switch, such coils being displaced relative to one another by ninety degrees. The motor switch is controlled by the cams rzkl and nk2, and executes large steps over its bank multiple which is subdivided into decades of contact groups. The second series of impulses then controls the motor switch by means of a suitable control relay (not shown) to execute individual steps so as to set its wipers upon selected bank contacts. The first series of impulses is at the same time transmitted by the contact a3 to the magnet D1 of a rotary switch, and the second series of impulses is similarly transmitted to the magnet D2 of a rotary switch by way of contact a3 and a contact n3 of a switching relay U shown in Fig. 3b. The third series of impulses is transmitted to the magnet -Dg of a rotary switch by way of the contact a5 and actuated contact a3 of the.

first-mentioned switching relay U and also contact x3 of a second switching relay X shown in Fig. 3b, which has i meanwhile become energized. After the conclusion of the third impulse series, there is energized a switching relay Y (Fig. 3b) for actuating the contact y3 so that the additional series of impulses are transmitted to a mechanical impulse repeater IW where they are stored.

The switching of the contacts :13, x3, y3 by the relays U, X and Y is explained below with reference to Fig. 3b.

The line or impulse relay A which actuates responsive to receipt of the various impulse series (digits) and actuates the contact a3 (Fig. 3) also actuates contact a2 (Fig.

' 31)). Accordingly, a slow-tc-release relay V will be actuated during each impulse series. Contact 02 is a contact controlled by relay C (Fig. 3) upon seizure of the equipment by a calling line. Relay V closes contact v1 to energize slow-to-release relay M. Relay V restores at the conclusion of the first impulse series, closing contact v2 while contact m1 of relay M is still closed.

Relay U accordingly energizes and actuates its contact 113 (Fig. 3) to switch the impulse circuit from contact :13 to magnet D2. Relay U remains operated in a holding I circuit over its own contact 111.

Relay X is energized after the second impulse series during the deenergization interval of relay M, in a circuit from ground, a2, m2, v3, X, 02 to battery. Relay X actuates its contact x3 (Fig. 3) to switch the impulsing circuit from contact a3 over to the magnet Dg so that this L y the deenergization interval of relay M, in a circuit from ground x2, m3, v4, V, 02 to battery, closing a holding circuit for itself over contact 3 1. Relay Y also actuates contact y3 (Fig. 3) to switch the impulsing circuit from contact (13 to the impulse repeater 1W (see also Fig. 3a). Accordingly, the fourth and all further impulse series will be transmitted to the impulse repeater and stored therein.

Necessary details of a motor switch of a type having the field coils M1 and M2 may be had from consulting copending application Ser. No. 269,224, filed January 31, 1952, now Patent No. 2,701,824, dated February 8, 1955. Impulse storage and repeating devices that may be used in place of the device IW are likewise well known, and the corresponding device has therefore been indicated in Fig. 3 merely in a diagrammatic manner. U. S. Patent No. 2,188,461, dated January 30, 1940, describes a mechanical impulse repeater that may be easily modified for use as impulse repeater JW indicated in Fig. 3. The

pertinent parts are shown within the dot-dash rectangle I of Fig. 3a.

a ano the dot-dash rectangle are also shown in Fig. 3. They include the line relay A, a capacitor, relay RS, contact nsi, and contact i2 one side of which is connected to a bank contact of a switch wiper smIII. The contact nsi corresponds to a contact marked imp in Fig. 1 of the previously mentioned Patent No. 2,188,461. Below these parts are shown the contacts (13, I13, x3 and y2 and switch magnets controlled thereby, and also the switch magnet Da connected to a bank contact accessible to a switch wiper smII, all as shown in Fig. 3. The conductor extending from one side of the contact y2 and the conductor extending from wiper smII terminate respectively in receiving magnet RCM and over certain contacts in the transmitting magnet TRM of the known impulse repeater. MKM indicates a marking magnet and N indicates an oft-normal contact.

impulses are transmitted to the receiving magnet RCM of the known impulse repeater JW of Fig. 3 (dot-dash rectangle of Fig. 3a) over a circuit including contacts 113, x3, y2 of the relays X, U, Y (Fig. 3b). The operation of the transmitting magnet TRM is released responsive to closure of contact p2 by way of contact e3 and il.

in a manner which will be presently described more in detail. The transmitting magnet TRM, upon operating as described in Patent No. 2,188,461, causes actuation of the contact imp (Fig. 1 of the patent referred to), such contact being designated in Fig. 3 as nsi, to transmit digits of the wanted subscribers number.

Returning now to the description of Fig. 3, after the marking number 362 has been received, the wipers M1 and M2 of the motor switch belonging to the zoning switch will be in the position 36 and the wipers dg3 of the rotary switch Dg will be in position 2. Over the wiper M2 of the motor switch and the wiper dg3 of the rotary switch Dg there are connected the various zoning contacts, for example, 21 to Z4. In the present case the zoning contact z4 will be connected to the calling line. The direction of the call, which is determined by the stored marking number, is marked in the routing switch by the connections provided between the bank multiple accessible to the wiper M1 of the motor switch, the bank multiple accessible to the switch wiper dgl and the multiple scanned by the switch wiper d of the routing switch. Any line marked is at the same time the line over which the routing switch is caused to start its operation. The start relay H is common for all traiiic directions and therefore can operate only after receipt of the corresponding marking digits. High-ohmic resistors Wil, Wi2, Wi3 are provided in the branch start circuits to the relay H to prevent testing (seizure) of the routing switch in unmarked directions. Also associated with the zoning switch is a digit switch having the magnet Da and a control switch having the magnets Smv and Smr. Over the switch arm d'aII of the digit switch having the magnet Da is obtained the first digit 3 stored by the switch D1; over the arm daIII is obtained the second digit. 6 stored by the switch D2; and over the arm daIV is obtained the third digit 2 of the marking number which has been stored by the switch Dg, at a time when these digits are to be transmitted, as called for by a check-back signal sent out by the routing switch. The sequence of the digits to be transmitted is determined by the control switch having the magnets Smv and Smr which is a step-by-step switch capable of operating in two directions. The forward operation of this control switch is controlled by the switching magnet Smv and its reverse operation is controlled by the magnet Smr.

When the zoning switch in the switching office KA262 is seized by a preceding group selector for setting up a toll call in the direction of the switching office 362, there is at the same time seized the routing switch UW. The drive means of the routing switch is similar to the drive means M1 and M2 for the zoning switch and is illus trated in Fig. 3c. It comprisesthe field magnets or coils M35 and M4. After the storage or marker switch has been set, relay' H (Fig. 3) will be. deenergized as will be. presently described more in detail, to start the operation of the routing switch UW. The start circuit extends from ground, 04, mk4, field magnet M4, to battery. The contact mk4 is a cam contact of the switch which may be of the kind described in the previously mentioned Patent No. 2,701,824. The routing switch UW, during its operation, actuates alternately cam contacts mk3 and mk4. The routing switch hunts for an idle trunk QKl leading to the exchange 362 (Fig. 3), as will be-pr'esently described more in detail, and as soon as an idle trunk is found, the test relay P (Fig. 3) will be energized and will actuate its contact p1 (Fig. 3c) to energize both field magnets M3 and M4 simultaneously, thus causing the switch to stop. As will be presently described, if the routing switch does not find an idle trunk in the corresponding trunk group, it will hunt in the next trunk group. Between the bank contracts of the respective trunk groups are disposed bank contacts for control purposes (contacts R1, R2, R3 in Fig. 3). The relay P will energize when the switch wipers engage these control contacts and will stop the switch by closing its contact p1 (Fig. 3c) as described. A relay Q (Fig. 3) will also be actuated together with relay P. Relay Q actuates a contact q2 (Fig. 3), thereby short-circuiting relay P to.

ground at contact s controlled by a relay S (Fig. 3c). Relay P accordingly restores and the routing switch continues to hunt in the next group of trunk lines. Relay Q upon energizing also closes contact q3 (Fig. 3c) to conmeet two differential windings I. and II of relay S which is slow-to-operate. The functions of relay S will be presently explained more in detail.

As has been indicated before, after receipt of the marking digits, the routing switch which is started by the operation of the relay H first hunts in the group of direct interofiice trunks QKI leading to the desired switching office 362. As soon as an idle trunk line is found in this group, the relay P of the routing switch will energize from ground, M1 in position 36, Dgl in position 2,

switch arm d of the routing switch, winding of relay P, switch arm c of the routing switch, trunk line 362 to battery. Relay P causes deenergization of a slo -to-release relay which controls the contact w. This slow-torelease relay has not been shown, because it is known and would merely encumber the drawing. After its release there is closed a start circuit for the impulse repeater IW over contacts p, w, switch arm smdl of the control switch in position 0 thereof. The impulse repeater starts the transmission of the remaining digits of the called sub scribers number which, in the assumed example, are the digits 4, 3, 5, 7. If the routing switch UW does not find an idle trunk in the trunk group QKl, it will continue to hunt in the next trunk group QK2. Between these groups are disposed the previously mentioned check-back contacts R1. When the switch arrns d, c of the routing switch engage the contacts R1, the relay Q will be energized from ground, R1, d, P, c, Q to battery. Relay P also energizes in this circuit and exerts a braking action on the switch so as to permit the relay Q to energize. However, relay P is immediately shunted over contact q2 so that the switch can continue its hunting operation. Relay Q closes at its contact g3 (Fig. 3c) a circuit for the differential windings of relay S which opens its contact .5 (Fig. 3) to deenergize relay Q. Ground is connected to the magnet Smv by contact g1, thus giving this magnet a control impulse. The control switch moves its wipers smI and smII into position 1. The routing switch UW continues hunting in the next trunk group QK2 containing the interofiice trunk lines to :the main exchange HA36. A slow-to-release relay (not shown) becomes: deenergized after conclusion of the hunting period, thus closing contact w to complete the circuit for the rotary magnet D0 of the digit switch when the routing switch finds an idle trunk in the group QK2. The circuit extends from ground,

p2, w, e3, :1, smII, Da to battery. It may be mentioned,

and deenergizes 11 that in such a case'the test relay P of the routing switch is energized over the switch arms d, c of the routing switch and the seized trunk in a manner described before.

If no idle trunk is found by the routing switch UW in the trunk group QKZ, it will continue hunting in the next trunk group QK3. The relay Q is again energized when the switch wipers d and c reach the check-back contacts R2, and the magnet Smv of the control switch receives another impulse to move its wipers smI and smII into position 2. If there is no idle trunk in this group, the routing switch UW will continue hunting in the bank multiple containing contacts of the principal trunks RL which lead to the own main exchange HA26. Upon transition from the third to the fourth trunk group, the relay Q will again receive an impulse in the check-back position R3 of the wipers d and c of the routing switch UW. Magnet Smv of the control switch will accordingly also receive an im pulse and the control switch wipers smI and smII will assume position 3.

It shall now be assumed that the routing switch has found an idle trunk in the last trunk group RL. The test relay P energizes from ground, switch arm d of the routing switch UW, P, switch UW arm of the routing switch UW, to battery on the seized trunk line RL. Relay P causes, as before, deenergization of the slow-to-release relay (not shown) which controls contacts w, and afiter the release of such relay closes the following circuit for the rotary magnet Da of the digit switch: ground, p, w, i1, smII, Dr: to battery. The rotary magnet Da energizes and connects over its contact da a circuit for the energization of relay J. Upon energizing, relay I interrupts at its contacts ii the circuit of the rotary magnet Daof the digit switch, causing this magnet to deenergize and to open its contact da, thus causing deenergization of relay J which restores its contact 11 to reenergize magnet Da. The digit switch is thus operated step by'step by interplay of the magnet Da and the relay 1. The wipers M11 and smII of the control switch are in position 3, and the digit 3 which has been stored by the wiper de controlled by magnet D1 is now released to operate relay T. A ground impulse is given to the main exchange at each step of the digit switch over the contact i2 and the wiper smlII of the control switch. After three steps and consequently three impulses to [the main exchange, the relay T will energize from ground, d1 in position 3, daII inposition 3, sml in position 3, T to battery. Relay T closes its contact t, giving an impulse to the magnet Smr which is operative to rotate the wipers smI and smII in reverse direction into position 2. The switch Da is in the meantime quickly restored to normal in a circuit extending from an interrupter Uni, contact 12 of relay T, wiper daI, and slowato-operate relay E. This circuit is after deenergization of relay T maintained over contact c1 of relay E. The circuit is interrupted when wiper daI returns to normal. A new circuit is now eifective for Da which extends from ground, p2, w, e3, i1, smII, Da, to battery.

The magnet Da of the digit switch has in the meantime restored its wipers daII, daIII and daIV to normal position by suitable known means, not shown in the drawing. It begins to rotate again and by means of its wiper daIII releases the digit 6 of the marking number, which has been stored by the wiper d2 controlled by magnet D2. An impulse is transmitted to the main exchange at each step of the digit switch by means of the contact i2 of the relay J as before. After the wipers daII, daIII, daIV of the digit switch have moved by six steps, the relay T will again momentarily energize over the wipers d2, dull and switch wiper smI in position 2. Relay T gives an impulse to the magnet Smr of the control switch to rotate its wipers another step in reverse direction so as to assume position'l.

The digitswitch (magnet Da), which meanwhile has again'returned to normal, again starts to rotate in order r 12 to release over its wiper daIV the digit 2 of the marking number which had been stored by the wiper dg3 controlled by magnet Dg. A current impulse is again transmitted to the main exchange HA26 by the operation of contact i2 incident to each step of the digit switch. Relay T energizes again after two steps over the wiper sml in position 1, wiper daIV in position 2 and wiper dg3 in position 2. The magnet Smr again receives an impulse to drive the wipers of the control switch into normal position.

in this normal position, there is connected over the wiper smlI of the control switch the impulse repeater IW which now transmits the remaining digits of the called subscribers number. The corresponding impulses are transmitted as ground impulses by the contact mi.

The seizure of the principal trunk RL by the routing switch WU in the call-originating switching office KA262 causes seizure of a similar routing switch UW in the main exchange HA26. After conclusion of the hunting for the idle trunk line RL takes place the transmission, as above described, of the series of impulses of the marking number, beginning with its first digit. The impulses are received in the main exchange by the relay AH and are re-transrnitted over its contact ah to the rotary magnet Dml of a rotary switch having the wiper dm l. Upon conclusion of the first impulse series takes place a switch ing over operation to the rotary magnet Dm2 of a second rotary switch (having wipers dmZ) by the energization of a relay (not shown) which actuates the contact xa. The magnet Dm2 of the rotary switch receives the second impulse series. The third impulse series is also received by the rotary magnet Dm2, but there is a coincident switching to another wiper of the switch by the relay U. The switch executes a corresponding number of steps.

The digits received by the storage switches controlled by magnets Dml and D1112 mark in the routing switch UW in the main exchange the desired direction to the called switching office KA362. The routing switch opcrates after receiving the digits of the marking number in the same manner under the control of a start relay H as the routing switch in the call-originating switching The test relay PH of the routing switch operates from ground, wiper a'ml in position 3, n1, wiper dmZ in position 62, wiper f of the routing switch, PH, wiper e of the routing switch, trunk line 362 to battery, as soon as an idle trunk is found in the trunk group leading directly to the desired switching office KA362. Relay PH stops the routing switch and switches the line conductors through. The impulse repeater IW of the call-originating switching office thereupon transmits by means of contact usi the remaining digits of the called subscribers number.

If the routing switch does not find an idle trunk in the trunk group QHI, it will continue hunting in the next trunk group QHZ. Between the bank contacts of the two trunk groups are again provided the check-back contacts R1 over which a circuit is closed for the energization of relay QB when the wipers f and e of the routing switch pass from the first to the second group, the circuit extending from ground, R1, wiper 1, PH, wiper e, R1, QB to battery. The relay PH energizes momentarily. The relay QB opens its contact lqb, thereby disconnecting the impulse relay AH from the line, and closes its contact Zqb to transmit a brief battery impulse back over the line which is received by the relay RS in the zone switch disposed in the call-originating office KA262.

Relay RS closes its contact rs, thereby closing a circuit for the magnet Smv of the control switch. The latter moves its wipers from position 0 to position 1. Whenever the relay RS operates, it causes energization of a slowto-release relay which controls the contact w. After conclusion of the hunting period of the routing switch in the main office HA26, if there is no more check-back impulse, there will thus be completed a circuit for the magnet Da of the digit switch from ground, p, w, i1, smII, D'a to battery. The digit switch scans in position 1 of the wiper smI control switch the third digit (2) of the marking number and transmits a corresponding number of impulses to the main exchange HA26. Relay PH of the routing switch in the main exchange HA26 operates during the hunting period from ground, dml, ul (position 36), PH, e, line 36 to battery. Relay PH stops the routing switch and switches the line conductors through.

If the routing switch does not find an idle trunk in the trunk group QHZ, it will continue hunting in the trunk group QH3. When the wipers f and e pass over the checkback contacts R2 (disposed between the bank contacts of the two trunk groups) the relay QB will again energize and will transmit a battery impulse back to the call-originating switching office KA262, which will cause energization of relay RS, as before. The latter relay again energizes the magnet Smv control switch to step its wipers by one step, from position 1 to position 2. If there is no further check-back impulse during the interval when relay RS causes the deenergization of the relay having the contact w, the magnet Da of the digit switch will again operate (it being assumed that the routing switch in the main exchange has meanwhile found an idle trunk) from ground, p, -w, 11, smII, Da to battery. The digit switch senses the second digit (6) of the marking number over its wiper daIH and causes transmission to the main exchange of a corresponding number of impulses as described before.

Relay T in the zone switch of the call-originating ofiice KA262 is actuated after the digit switch has transmitted the second digit. It closes a circuit for the reverse magnet Smr of the control switch. The latter executes a step in reverse direction and moves its wipers from posi tion 2 to position 1. Thereupon is again completed a circuit for the magnet Da of the digit switch (which meanwhile has returned to normal) from ground, p, w, i1, smII, Da to battery. The digit switch now operates to sense the last digit (2) of the marking number, causing transmission of a corresponding number of impulses to the main exchange HA26, as before. Relay T again operates after the transmission of this digit to actuate the control switch from its position 1 to position 0. The circuit for the magnet Da of the digit switch is thus interrupted.

If the routing switch does not find an idle trunk in the trunk group QH3, it will continue hunting in the group of principal trunks RL leading to the central district exchange ZAZ. Upon passing from the trunk group QH3 over the check-back contacts R3 to the trunk group RL, the routing switch will transmit another check-back impulse to the zone switch in the call-originating office. This impulse again energizes the relay RS which causes the magnet Smv of the control switch to move wiper smI from position 2 to position 3. The relay controlling the contact w is at the same time caused to deenergize.

If it is now assumed that the routing switch in the main exchange HA26 finds an idle principal trunk line RW .to the central district exchange ,ZAZ, there will be a circuit closed (after closure of contact w) for the magnet Da of the digit switch Da from ground, p, w, i1, smII, Da, to battery. The digit switch thereupon quickly restores its wipers to normal. The control switch magnet Smv steps the corresponding wipers from position 3 to position 2. The magnet Da of the digit switch is then reenergized in the previously described circuit. The second digit (6) is now sensed by the wiper daIII and the control switch wiper smI moves thereafter from position 2 to position 1. The digit switch moves its wipers again to normal position and is subsequently again operated as described, to sense the third digit (2) of the marking number. The control switch magnet Smv thereafter moves the wiper smI from position 1 to position 0, and the digit switch magnet Da returns the corresponding wipers to normal. The circuit for the impulse repeater IW is now completed over the wiper smIl to transmit the remaining digits of the called subscribers number.

The transmission of the first digit 3 of the marking number causes the setting of group selector ZGW in the central district exchange 2A2 on the trunk of the associated routing switch UW which is similar to the correspondingly marked routing switches described before. The two subsequent digits (6, 2) of the marking number are received by and stored in the coacting rotary switches having the magnets Dm3 and Dm4. The stored number 62 marks in the routing switch of the central district exchange the desired direction to the wanted switching office KA362. The routing switch, which is in this case preferably a four-conductor motor switch having several switch arms (such as disclosed in the copending application Ser. No. 269,224, filed January 31, 1952 now patent No. 2,701,824) begins to operate after the last two digits of the marking number have been received by the associated rotary switches Dm3 and Dm4, and hunts for an idle trunk, first in the trunk group QZl leading to the desired switching ofiice KA362. If an idle trunk is found, the relay PZ will operate from ground, dm3 (position 6), dm4 (position 2), g, PZ, k, trunk line 62 to battery. The remaining digits 4, 3, 5, 7 of the desired number are now received from the impulse repeater IW of the calling switching office for the setting of the switches in the called oflice and its subexchange.

If the routing switch in the central district exchange ZA2 does not find an idle trunk in the trunk group QZl, it will continue to hunt in the trunk group QZ2 leading to the associated main exchange. A check-back impulse is again transmitted to the call-originating office KA262 by the operation of relay QC when the wipers g and k of the routing switch pass over the check-back contacts R1 which are disposed between the bank multiple contacts of the two trunk groups, so as to cause operation of the relay RS in the call-originating ofiice. Means may of course be provided in the central. district office to transform the impulse so as to transmit over the connection that has so far been built up an alternating current impulse or a sound frequency impulse, and suitable means may be provided in the call-originating oflice to re-transform such alternating current or sound frequency impulse to a direct current impulse for the operation of the relay RS. Such means have not been shown because they are well known in the art. The magnet Smv of the control switch in the call-originating ofiice KA262 is actuated responsive to the operation of relay R3 to move its wipers from position 0 to position 1, as described before, thereby preparing for the re-transmission of the last digit 2 of the marking or district numher at a time when the routing switch in the central district exchange finds an idle trunk in the trunk group QZ2.

However, if there is no idle trunk in the trunk group QZ2, the routing switch in the central district exchange ZAZ will continue to hunt in the group of principal trunks RL leading to the central district exchange ZA3. A check-back impulse is again transmitted when the wipers of the routing switch in the exchange ZAZ pass from the trunk group QZ2 to the trunk group RL, by the operation of the relay QC, over the circuit involving the switch wipers g and k and the check-back contacts R2 to actuate the relay RS in the call-originating ofiice KA262, as before, so as to operate the magnet Smv of the control switch to prepare for the re-transmission of the two last digits of the marking number, which are transmitted when an idle trunk RL to the central district exchange ZA3 is found.

If such idle trunk is not found, the routing switch in the central district exchange ZAZ will continue hunting in a trunk group RL2-4, forming by-pass trunks to the central district exchange 2A4. Three check-back impulses are in this case transmitted back to the call-originating office KA262, which are received by the relay RS to cause the associated magnet Smv of the control switch to operate so as to move its wipers from position 2 to position 3, thereby preparing for the re-transmission of the entire marking or district number 362. The first digit 3 of the marking number is transmitted by the impulse storage device JW of the call-originating office KA262 at the conclusion of the hunting period of the routing switch in the central district exchange, that is, at the time when thisrouting switch finds an idle trunk line RL2-4 to the central district exchange ZA4, thereby seizing a group selector ZGW in such exchange. This group selector is by this digit 3 set on a trunk line to the central district exchange ZA3, thereby seizing a group selector HGW. See also Fig. 2. The next digit 6 transmitted from the call-originating o ifice KA262 sets the group selector in the central'district exchange ZA3 to seize a trunk line to the associated main exchange HA36, thereby seizing the group selector KGW. The last digit 2 of the marking number finally causes operation of the group selector KGW to seize a trunk line to the switching office KA362, which terminates in the selector EGW. The remaining digits, which are thereupon transmitted by the impulse repeater 1W of the call-originating office KA262, set the group selector EGW of the desired switching office KA362, and finally the switches of the associated subexchange EA, to complete the call to the desired subscriber number 3624 -357.

The release of the connection has no bearing on the invention, and description thereof has therefore been omitted.

The separation of the impulse-repeating means in the call-originating exchanges into means for repeating only the direction-determining marking or district number and means for transmitting the remaining digits corresponding to the called subscribers local number gives the possibility to re-transmit the marking numbers by suitable and known means in a different form, for example, in accelerated sequence or in the form of codes. The time required for completing connections can thereby be appreciably shortened.

It should be observed that it is not absolutely necessary to associate the zoning means in the call-originating offices individually with the corresponding routing switches. If desired for reasons of economy or the like, these means may be disposed centrally, and such central zoning means may transmit the marking determined by a stored marking or district number, for example, by impulses, to individual marking equipment.

It is likewise not absolutely necessary to repeat only part of the digits of a marking district number, as described. If desired, the digits of the entire directiondetermining number may be re-transmitted and impulse repeaters may be provided in the various switching exchanges, which suppress unnecessary digits.

It may be mentioned in conclusion that the zoning switch in the call-originating exchanges (which is used, as described, as a marking switch for the associated routing switch) is in usual manner employed for metering the toll calls.

Changes may be made within the scope and spirit of the appended claims.

What is claimed is:

1. In a multi-exchange automatic telephone system having a plurality of exchanges of different classes and direct and detouring trunk lines disposed therebetween for setting up connections extending from an originating exchange through intervening intermediate exchanges to a destination exchange, impulse storing means in a call originating exchange for receiving and storing impulses corresponding to digits of a called line desired in a toll call, means in said intermediate exchanges responsive to extending a toll call thereto for transmitting difierentiating check-back signals to said impulse storing means in the call originating exchange, said check-back signals being characteristic of the class of trunk lines momentarily available in the corresponding intermediate exchange for extending the respective toll call to the destination exchange, a control switch for governing the sequence of digits to be transmitted responsive to said check-back signals, and repeater means cooperating with said storing means in the call originating exchange for transmitting to the corresponding intermediate exchange over said control switch only that part of the stored impulses corresponding to digits required for extending the respective toll call to the destination exchange.

2. The circuit arrangement defined in claim 1, comprising a switch in said intermediate exchange, said switch having access: to a first group of trunk lines leading directly to the called exchange; to a second group of trunk lines leading to a distant main exchange interconnected with the called exchange; to a third group of trunk lines leading to a central exchange of the district of the called subscriber; and to a fourth group of trunk lines leading to a central exchange of another district; said means for transmitting characteristic check-back signals being operative to omit transmission of such signals when said routing switch selects a trunk line in said first group and to transmit, respectively, one, two or three checkback signals when said routing selector switch selects a trunk line in the second, third or fourth group, respectively.

3. The circuit arrangement defined in claim 1, wherein impulse storing means in the call-originating exchange which is responsive to said check-back signals includes a control switch having switch wipers coacting with contacts on which the stored digits have been marked, said control switch being operative to operate said switch wipers in forward direction responsive to receipt of a check-back signal and thereafter in reverse direction to prepare for the re-transrnission of said stored digits. 7 v

4. A toll call district telephone system comprising a toll call-originating exchange, toll call routing switch means in said call-originating exchange having access to trunk lines leading directly to the exchange nearest to the called subscriber and to groups of trunk lines leading to other exchanges, each of said other exchanges having toll call routing switch means which have similar access to similarly directed trunk lines, digit impulse storage means in the call-originating exchange for storing the digits of a called subscribers line including the digits. which designate the district number thereof, means con-.

trolled by each toll call routing switch in each exchange for transmitting differentiating check-back signals to the toll callvoriginating exchange, a control relay responsive to said check-back signals, and means controlled by said control relay for controlling said digit impulse storage means to transmit digits of the called subscribers line depending on the trunk routes selected in the progressive building up of a toll call.

References Cited in the file of this patent UNITED STATES PATENTS 2,339,709 Ostline Ian. 18, 1944 2,431,313 Hertog Nov. 25, 1947- 2,554,155 Molnar May 22, 1951 2,597,209 Walsh May 20, 1952 2,631,195 Ostline Mar. 10, 1953 

